It refers to the process of exposing a newly manufactured or repaired product or component (typically electronic) to stresses such as thermal cycling and vibration in order to force latent defects to manifest themselves by permanent or catastrophic failure during the screening process.

Basically, the life of all electronic products can comply with Bathtub curve, which includes three parts as following;

1．The first part is a decreasing failure rate, known as early failures.

2．The second part is a constant failure rate, known as random failures.

3．The third part is an increasing failure rate, known as wear-out failures.

Below images shows the relationship between environmental stress and electronic products failure. You can find temperature and humidity are the biggest effect in electronic products.